Tiny Reverse GeoCache

GeoCaching is a high-tech treasure hunting game (sport?) with GPS system involved. By using a hand-held GPS receiver the user has to go to a specific coordinate to obtain a hidden treasure which is usually a container with fun stuff inside. Reverse GeoCaching is relatively new thing where the idea is that you already have the treasure in your hands, but in order to access it you must go to a specific location. Once you get there, the box opens and the treasure is yours. The box doesn't show you the destination coordinates but only the distance and also a limited number of clues and that's where the fun starts.

This Reverse GeoCache Box is pretty nicely engineered and built. The hardware that makes it all work is: MAX1674 step-up converter, Haicom HI-204 SiRFStar GPS receiver, PIC18F2520 microcontroller and other bits and pieces. The software is written in C and it used 10kWords of 16kWords available in the PIC.

AVR tutorial - External Interrupts

External interrupts are a core part of AVR I/O and they work a bit like interruptions in real life. Consider what happens when you read a book and the phone rings. You place a bookmark, answer the phone, then get back to the book, picking up where you left off.

Protostack just published a tutorial which explains how AVR microcontrollers deal with such interruptions. It covers both external and pin change interrupts. Like other Protostack tutorials it has plenty of detail and code examples.

Biennophone radio from 1953 with mp3

This is a very old Swiss-made HF radio from 1953 called Biennophone that used to receive radio stations via telephone line. Yes, the good old telephone line! That service was operating in Switzerland from 1940 to 1998 when it was finally terminated.

In order to keep the radio operating, it needed a new source of signal. Also, to keep the sound quality of the old times this radio incorporates home built AM tube radio receiver with FM receiver, mp3 player and AM modulator to send the signal to the AM tube radio on last two channels 340 and 307 KHz. See the build images and description after the break.

Connecting thermal printer with AVR

This is actually a thermal printhead, not a printer. Connecting a printer would be much easier; just send it some AT commands and it will print your data. In this case the author had to implement "font" in firmware, control two servo motors and the burning dots on the printhead itself.

The microcontroller of choice is AVR with Arduino bootloader. The burning dots (heating elements) are controlled with ULN2801A darlington transistors array which is in turn controlled by SN74164 shift register to save many IO pins. See the video of the printer in action after the break.

POV Propeller Clock Build

Here are a few pictures and videos of the latest project of our forum member [Kizo].

It is a POV propeller clock and it just might be the best one yet! Firmware is written in Bascom-AVR and consists of around 3000 lines of code. The power between the motor and the rotating electronics is transferred wirelessly (see the second video).

Nixie clock in a model train

This Nixie Clock comes from [pezi666999] from Germany and it is originally a single nixie tube clock but in a slightly different housing.

The clock is put inside a model train (a model locomotive) and the tube is actually IN-8-2 with "dot mark" not used. You can see how it works in the video after the break, and you can also take a look at the original project page to make one yourself.

Digital clock/calendar/thermometer

Be sure not to miss this great digital clock with built-in calendar and thermometer!

This is a relatively small digital clock/calendar with thermometer based on Microchip PIC16F628 (or even PIC16F84) and DS18S20 or DS18B20 temperature sensor from Maxim-IC. The hardware part is very simple because it only uses PIC microcontroller, DS18S20/DS18B20 sensor, 4x7 segment LED display with common anode, four 2N3906 transistors, and some resistors.

New version of Protostack AVR board

This week Protostack released version 1.5 of their AVR development board. Like the previous version that we reviewed back in January, this one comes with a range of improvements... 6 in fact.

The power supply section has been updated to support voltage regulators with Input/Ground/Output pinouts and Ground/Output/Input pinouts. This is achieved by using 4 plated through holes (I G O I) and a strange looking figure of 8 shaped mounting hole. The new power supply block also includes a diode and resettable fuse to protect against reverse polarity and over current.

With better port labelling, a bigger dual row block and better labelling for a CR2032 battery connector, this improves what was already an excellent development board.